How to get stars with a plus sign.

I have a potentially dumb question. I see all these images of sharp stars with light rays making a plus sign. Any pointers on whether this is post processing or acquisition?

how does one manage to work towards that?

appreciate the help and points.

-Thanks,
Kapil K.

Hello Kapil,
There are two ways to get these '+' artifacts on your stars. One of them is a physical product of Newtonian telescopes that have a secondary mirror supported by a 'spider', a 4-vaned brace that supports the secondary mirror. The second way is a little trick done with thin pieces of dark string. I use this method on my Schmidt-Cassegrain telescope because it does not have a secondary 'spider' due to its design. I enjoy the look of the 'star point' artifacts on the brighter stars in my images. You simply tape two pieces of thin, dark string across the front aperture of the telescope at right angles to each other. Be sure to use dark string or thread, so as not to introduce unwanted reflections.

Hope this helps,

- - Steve

Thanks Steve. Would this trick work on refractor telescopes? I usually image with refractors.

I've never tried on a refractor, Kapil, but I don't see any reason why it wouldn't work. Depending on the size of your refractor (I have an 80mm piggy-backed on the big scope), I would recommend using very thin string - maybe black fly-fishing line. This is what I use on my 11-inch, and my recent post of NGC-2403 shows the results on the brighter stars.

Hi,

It's interesting to see that one wants to add an artifact from something that doesn't need to be there. That's not supposed to be a critique but it just surprises me.

I just want to add one thing to consider before you're adding the diffraction pattern to your image: if you're going to combine images from different sessions you may end up with not just the "+" around the star but literally with a star. If you cannot guarantee a perfect rotational alignment, the orientation of the diffraction pattern will likely vary.

If you want to add this artificial artifact, I would consider to search if there are some software tools that may add it during post processing.

CS!
BJörn

Björn Arnold:
If you want to add this artificial artifact, I would consider to search if there are some software tools that may add it during post processing.

*For fear of being one of those forum participants who knows nothing about the topic I am about to add too, I will add that I have read in some Descriptions from contributors of images containing diffraction spikes that they added using software. I just wanted to state this in case someone who does know exactly how to do this fails to respond here. Otherwise it will be up to you to choose your method. My bet is a quick search on the internet will solve the software question very quickly.

Björn Arnold:
Hi,

It's interesting to see that one wants to add an artifact from something that doesn't need to be there. That's not supposed to be a critique but it just surprises me.

I just want to add one thing to consider before you're adding the diffraction pattern to your image: if you're going to combine images from different sessions you may end up with not just the "+" around the star but literally with a star. If you cannot guarantee a perfect rotational alignment, the orientation of the diffraction pattern will likely vary.

If you want to add this artificial artifact, I would consider to search if there are some software tools that may add it during post processing.

CS!
BJörn

Diffraction spikes are only affected by polar alignment, assuming you do not rotate the scope inside its rings.

Diffraction spikes are only affected by polar alignment, assuming you do not rotate the scope inside its rings,

Absolutely. But I’ve seen images where people put data together with a year in between and obviously something has changed since stars had 8 spikes. Especially if one wants to make artificial spikes during exposure, the self made solution needs to consider this.

Thanks folks. Whether I do this as a practice or not is not the core part of the question. It is more out of curiosity and experimentation. I also think it should be the photographer’s choice and discretion on what artifacts they want to add in their images. No one is forced to like any image they don’t like 😊.

I was more thinking that there might be a post processing script or something that might be worth trying out. I have also seen unprocessed images have them. Which is why Steve’s explanation makes a lot of sense (thanks Steve!). I’ll try out other forums and methods to gather this info as well!

Kapil K.:
I have also seen unprocessed images have them. Which is why Steve’s explanation makes a lot of sense (thanks Steve!)

By the way, they’re not just becoming visible in images. If you’re observing visually, you can also see the spikes if you’re pointing at bright enough stars.

Found this interesting article: https://wonderdome.co.uk/pointy-stars-diffraction-spikes-explained/

apparently there is a photoshop plugin called “StarSpikes PlugIn for Adobe Photoshop”

If you're really wanting them I would just go the post processing route. You linked above. Plenty of options/settings.

I've added stars spikes to my 80 mm refractor for the same reason, I enjoy the look of the diffraction artifacts.

Made a simple cardboard tube that fits the dew shield, and attached some thin metal wire to the cardboard using tape.

You can see the result in this image of gamma Cas:
(Mouse-over shows data without the spider)

IC59 / IC63 - Ghost of Cassiopeia HaRGB

A real Newtonian or RC telescope will produce slightly different spikes, it's almost a fingerprint of the telescope's mechanical design.

Once upon a time people went to great lengths getting RID of diffraction spikes. This is kind of funny to think of.

I used the StarSpikes PlugIn for Adobe Photoshop on my image and this is the result I got. It is pretty cool, you can play around with various settings to increase/decrease the number of stars as well as intensity, spike lengths, etc.

Photoshop plug-ins, see link

https://prodigitalsoftware.com/Products.html

Sample view of diffraction spike options. Part of the Astronomy tools, Carboni's actions.

Bob Lockwood:
Photoshop plug-ins, see link

https://prodigitalsoftware.com/Products.html

Sample view of diffraction spike options. Part of the Astronomy tools, Carboni's actions.

Pretty cool. Thanks Bob. I did compare the Astronomy tools vs StarSpikes PlugIn. Astro tools is fairly basic and I couldn't find a way to tweak the settings. I really liked the flexibility and customization one can get with StarSpikes Plugin.

Kapil K.:
Bob Lockwood:
Photoshop plug-ins, see link

https://prodigitalsoftware.com/Products.html

Sample view of diffraction spike options. Part of the Astronomy tools, Carboni's actions.

Kapil K.:
Pretty cool. Thanks Bob. I did compare the Astronomy tools vs StarSpikes PlugIn. Astro tools is fairly basic and I couldn't find a way to tweak the settings. I really liked the flexibility and customization one can get with StarSpikes Plugin.

The difference in the two is with the Astronomy tools you get 34 action tools, and yes, there pre set actions, you can’t adjust them, but there not meant to be adjusted, where the StarSpikes 4 pro is just for diffraction spikes.

Bob Lockwood:
Kapil K.:
Bob Lockwood:
Photoshop plug-ins, see link

https://prodigitalsoftware.com/Products.html

Sample view of diffraction spike options. Part of the Astronomy tools, Carboni's actions.

Kapil K.:
Pretty cool. Thanks Bob. I did compare the Astronomy tools vs StarSpikes PlugIn. Astro tools is fairly basic and I couldn't find a way to tweak the settings. I really liked the flexibility and customization one can get with StarSpikes Plugin.

The difference in the two is with the Astronomy tools you get 34 action tools, and yes, there pre set actions, you can’t adjust them, but there not meant to be adjusted, where the StarSpikes 4 pro is just for diffraction spikes.

Yup. I use to use astronomy tools quite extensively before I switched to Pixinsight. I still sometimes process end to end in photoshop and the tools come in real handy!

In case anyone is interested in a comparison. I used my old Pleiades image and played around with settings on StarSpikes and created two contrasting versions. If you are into this, the flexibility is enormous:

Kapil K.:
Thanks folks. Whether I do this as a practice or not is not the core part of the question. It is more out of curiosity and experimentation. I also think it should be the photographer’s choice and discretion on what artifacts they want to add in their images. No one is forced to like any image they don’t like 😊.

True. However, if artifacts are added to an image I think that it should be made clear that they have been added and not let the viewer think that they are what came out of the camera.

I guess it's a matter of taste, but I think I prefer stars to just look like stars…

Telescopes come in 2 types, positive and negative. You need to buy a positive telescopes to get positive stars.

Matt ProulxTelescopes come in 2 types, positive and negative. You need to buy a positive telescopes to get positive stars.

Err.. not sure I get this joke...

Stuart Taylor:
Matt ProulxTelescopes come in 2 types, positive and negative. You need to buy a positive telescopes to get positive stars.

Err.. not sure I get this joke...

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